The present invention relates to processes for preparing 2,2,2-trifluoroethanol. In particular, the invention relates to continuous processes for preparing such product.
2,2,2-trifluoroethanol is a starting material for the synthesis of various products, including the inhalation anesthetic isoflurane (CF.sub.3 CHClOCHF.sub.2). Various processes have been disclosed for preparing 2,2,2-trifluoroethanol. For example, in Lawlor et al., U.S. Pat. No. 2,868,846, a process is disclosed in which 2,2,2-trifluoroethanol may be made by heating 2-chloro-1,1,1-trifluoroethane in a reaction medium which includes an hydroxylated solvent, with the reaction medium being maintained at a pH of between 3 and 10, for example, by having dissolved therein a salt of a weak acid. Lawlor et al. say that to bring about reaction, the reaction mixture is heated preferably at a temperature in the range of 175.degree. to 300.degree. C. and preferably under the autogenously developed pressure. All of the reactions specifically disclosed in the Lawlor et al. patent are performed in a stirred autoclave on a batch basis. Also, the products and unreacted 2-chloro-1,1,1-trifluoroethane in the Lawlor et al. examples are either directly distilled after substantial depressurization from the autoclave or the liquid product is fractionated with the 2-chloro-1,1,1-trifluoroethane and 2,2,2-trifluoroethanol being separately collected. Similar processes conducted on a batch basis are disclosed in Chemical Abstracts, Vol. 69, Abst. No. 51575y (1968); Chemical Abstracts, Vol. 99, Abst. No. 212148y (1983); and Chemical Abstracts, Vol. 100, Abst. No. 34138z (1984).
A two-stage method for preparing 2,2,2-trifluoroethanol is disclosed in Astrologes, U.S. Pat. No. 4,434,297. In the Astrologes process, 2-chloro-1,1,1-trifluoroethane is reacted with an alkali metal salt of a carboxylic acid in a substantially anhydrous aprotic solvent, e.g., N-methyl-2-pyrrolidone, to form the carboxylic acid ester of 2,2,2-trifluoroethanol and an alkali metal chloride. This ester is then reacted with an hydroxide or a basic salt of an alkali metal in water to form 2,2,2-trifluoroethanol and the alkali metal salt. The alkali metal salt is disclosed as then being recycled for further reaction. The Astrologes patent suggests that his process can be run continuously but gives no details in that connection. The patent makes clear that the Astrologes process should be performed at temperatures below 200.degree. C. and that it is desirable to maintain pressures below about 500 psig as Astrologes' reaction progresses. Moreover, all of Astrologes' examples indicate that long reaction times, typically of from 3 to 10 hours and longer are required.
Other more remote methods to produce 2,2,2-trifluoroethanol include, e.g., catalytic hydrogenation of: trifluoroacetic acid; trifluoroacetyl chloride; 2,2,2-trifluoroethyl trifluoroacetate; or trifluoroacetic anhydride. See, for example, U.S. Pat. Nos. 3,356,746, 3,356,747, 3,970,710 and 4,396,784 and Chemical Abstracts, Vol. 85, Abst. No. 123333y. Also, Gumprecht, U.S. Pat. No. 4,311,863, discloses that 2,2,2-trifluoroethanol can be a by-product of the reaction of 2-chloro-1,1,1-trifluoroethane or 2-bromo-1,1,1-trifluoroethane with alkali metal fluoride in the presence of water.
It is highly desirable to provide a process in which 2,2,2-trifluoroethanol can be prepared on a continuous basis in high yields by an efficient process and with a relatively simple way of recycling unreacted 2,2,2-trifluoro-1-haloethane and optionally the organic acid salt or acid form thereof.